Thanks Dottie, You answered my question wonderfully. We have a bunch of 16's, 17's, a 19 and one wildly random 14 on Comprehension (WISC IV) but I read in a different thread that comprehension questions are more open-ended and if the child was not inclined to elaborate then it can effect this score. I just get the feeling (knowing my son) that by the time they were into the questions in the 16 & 17 range he was already itching to get out of there and go home. All in all it doesn't really matter as a score is a score is a score and in the end it is just another clue on the way to finding out the best learning situation/level for your child.
Thanks for the answer!